obama spent a couple of hours practicing yesterday, as well. and has three days set aside for more practice. it's nicknamed debate camp. and near the end of camp, like now, it's a full-on mock debate. following the time rules, podiums the exact distance apart, and fill-ins for the opposition. neera tanden has played the role, preparing joe biden. >> it's only tense when they give the completely wrong answer and you have to correct them in the end. the goal is to make them feel that they're as real as possible. >> reporter: tanden believes romney has the harder chore. >> the idea that i'm anti-immigrant is repulsive. >> reporter: being aggressive against the president, drawing distinctions between the president, trying not to be nasty. >> i don't think i'm that bad. >> you're likable enough, hillary. >> thank you. >> reporter: and the president, who can become impatient, is probably being pushed in practice, as well. >> part of having a tough opponent in your mock is that you get that anger out in the mock. so that the president is relatively ca